Direct, indirect, and potential effects of salinity on the White Sands pupfish (Cyprinodon tularosa) (New Mexico)

The White Sands pupfish (Cyprinodon tularosa), a New Mexico state-listed Threatened species, occurs in four ecologically distinct habitats. Malpais and Mound Springs have relatively low salinities around 3.5, whereas Salt Creek and Lost River have salinities ranging from 13 to approximately 100. Salinity has direct and indirect effects on the White Sands pupfish. Within Lost River, low salinity areas are inhabited by larger fish, suggesting that low salinity provides optimal growth conditions. Pupfish life history traits, such as age structure, length, minimum reproductive size, and relative condition, differ among habitats. Most striking was a shift in age structure for introduced populations. Introduced populations contained younger fish, suggesting that the habitats of Lost River and Malpais Spring are not ideal for pupfish. Some of these life history differences may be attributable to habitat differences such as salinity, however, life history traits were also strongly correlated with trematode intensity. Pupfish trematode intensity was related to reduced lipid content and edema.; High salinity in certain habitats precludes the occurrence of snails and associated pupfish trematodes. In Salt Creek, a springsnail, the presumed secondary host for pupfish trematodes, can neither survive long-term exposure nor reproduce in salinities above 35. Thus, parasite abundance in fish may be indirectly mediated by environmental salinity.; Salinity also creates important constraints for the likelihood of invasiveness by exotic species. Because of low salinity, Mound Spring and Malpais Spring are vulnerable to invasion by exotic species such as western mosquitofish and virile crayfish. In a mesocosm experiment, the presence of mosquitofish and crayfish led to negative pupfish population growth. However, crayfish only caused negative population growth when crayfish were at relatively high densities.